Materials-processing often involves the deposition of films or layers on a surface of a substrate. One manner of effecting the deposition of such films or layers is through chemical vapor deposition (CVD). CVD involves a chemical reaction of vapor phase chemicals or reactants that contain the constituents to be deposited on the substrate. Reactant gases are introduced into a reaction chamber or reactor, and are decomposed and reacted at a heated surface to form the desired film or layer. There are different methods of CVD; the key distinguishing parameter among them is the type of energy input.
Oxidative chemical vapor deposition (oCVD) can simultaneously polymerize and deposit conjugated polymeric films in a controllable fashion. Moreover, polymers are deposited at low temperatures and without solvent; therefore, this method is compatible with virtually any substrate (that is, the deposition process is independent of the chemical nature and electrical conductivity of the substrates). In addition, the conformal nature of polymer films synthesized by oCVD can be employed uniformly to coat rough surfaces, including micro- or nano-structured substrates. And so, use of oCVD may prevent device shorting in a rough substrate and the method can be used for successful device fabrication on unconventional substrates, like paper. oCVD has been shown to grow uniform and conformal conducting polymers and copolymers on different substrates. Unlike vapor phase polymerization (VPP), where a substrate is pretreated with a layer of oxidant, oCVD involves simultaneous exposure of the substrate to the oxidant and monomer vapors, which makes oCVD more compatible with various substrates. Moreover, the use of vapor deposition removes the requirement that the polymer be soluble. Hence, monomers without soluble side chains can be explored, opening a wider range of materials for consideration as active layers. The simplicity of oCVD can further be extended to patterned films using shadow masking. Thus, synthesis, thin film growth, and patterning are achieved simultaneously, in a process termed “vapor printing.”
A second method of CVD is initiated CVD (iCVD). In an iCVD process, thin filament wires are heated, thus supplying the energy to fragment a thermally-labile initiator, thereby forming a radical at moderate temperatures. The use of an initiator not only allows the chemistry to be controlled, but also accelerates film growth and provides molecular-weight and rate control. The energy input is low due to the low filament temperatures, but high growth rates may be achieved.
Finally, plasma-enhanced chemical vapor deposition (PECVD) uses radiofrequency-induced glow discharge to transfer energy to the reactant gases. In certain circumstances one might chose PECVD over other CVD methods due to its higher deposition rates, and the greater ability to control refractive indices. A further advantage of the PECVD method is that the process can take place at temperatures under about 400° C. Furthermore, PECVD processes and systems provide other advantages, such as good adhesion, low pinhole density, good step coverage, adequate electrical properties, and compatibility with fine-line pattern transfer processes.
All of these techniques are useful and have industrial applications to deposition of conformal, pin-hole free functional polymeric thin films with controllable film thickness and functionalities. However, each methodology requires a separate vacuum chamber and associated costs to build and maintain the chamber. Additionally, the fabrication of a single device using all of these methods simultaneously or sequentially is challenging. For example, consecutive deposition on a substrate of three different thin films by iCVD, oCVD, and PECVD requires the operator to transfer the substrate from one chamber to another chamber. As a consequence, time and energy are wasted, and the substrate could be inadvertently exposed to ambient conditions, which is highly undesirable for certain applications.
Therefore, there exists a need for a reactor that is capable of performing all of the aforementioned CVD processes in a single unit chamber.